This invention relates to an outboard motor engine and more particularly to a balancing arrangement for a reciprocating machine.
As is well known, reciprocating machines have certain forces which are inherently unbalanced. These are caused by such actions as the mass of the piston and connecting rod reciprocating to transmit drive between a crankshaft on which the connecting rod is journalled and the piston. Normally it is the practice to employ counter weights on the crankshaft so as to balance at least some of these reciprocating masses. However, it is also desirable to provide other means of balancing such as balancing shafts which also have eccentric masses and which are driven so as to rotate at the same speed but at an opposite direction as the crankshaft for balancing purposes. Although these balancing arrangements have a number of advantages, they do present problems in connection with engine design.
This is particularly true when the engine is employed as the power source for a marine propulsion unit such as an outboard motor wherein compact construction is desired. In order to avoid the churning of the lubricant in the crankcase chamber, it has been proposed to position the balancer shaft at one end or the other of the engine and to drive it from the crankshaft. This removes the balancer mass from the crankcase and avoids the problems with the lubricant. However, this has the effect of increasing the length of the engine which is not desirable in an outboard motor. It is desirable in an outboard motor to keep the length of the engine as short as possible so as to maintain a relatively low center of gravity for facilitating tilt and trim operation of the outboard motor.
Another disadvantage of providing the balancer shaft at one end of the engine is that the external portion of the engine does not afford the same degree of rigidity as the area in the crankcase and the support for the balancer shaft and balancer mass presents problems which can add to the overall size and weight of the engine.
If the balancer shaft and balancer masses are positioned in the crankcase chamber, on the other hand, then engine tends to become enlarged in the fore and aft direction when employed with an outboard motor. This also is undesirable because it is preferred to keep the size of the engine as small as possible since it must be contained within a protective cowling and it is also desirable to maintain the top end of the outboard motor very compact.
It is, therefor, a principle object of this invention of this invention to provide an improved balancing arrangement for an outboard motor.
It is another object of this invention to provide a balancer arrangement for a reciprocating machine that will provide a compact construction and yet nevertheless be robust and have good support and excellent balancing characteristics.